Windows Forms: r/w file

Form1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO;

namespace Datei
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            FileStream fs = new FileStream("test.dat", FileMode.Create, FileAccess.Write);
            StreamWriter sw = new StreamWriter(fs);
            sw.WriteLine(textBox1.Text);
            sw.Close();
            fs.Close();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            FileStream fs = new FileStream("test.dat", FileMode.Open, FileAccess.Read);
            StreamReader sr = new StreamReader(fs);
            textBox1.Text = "";

            while (sr.Peek() != -1)
            {
                textBox1.AppendText(sr.ReadLine() + Environment.NewLine);
            }

            sr.Close();
            fs.Close();
        }
    }
}